In an information recording medium, such as a DVD-ROM (DVD-Read Only Memory), a DVD-R (DVD-Recordable), and a BD-ROM, there is also developed a multilayer type or dual-layer type optical disc or the like on which a plurality of recording layers are laminated or bonded on a same substrate, as described in patent documents 1, 2 or the like. (Comment: a CD may have no dual-layer disc, so the DVD and the BD are exemplified.) Moreover, if recording is performed on the dual-layer type, i.e. two-layer type optical disc, e.g. a two-layer type DVD-R disc, an information recording apparatus, such as a DVD recorder, focuses a laser beam for recording on a recording layer located on the front side (i.e. on the closer side to an optical pickup) viewed from the irradiation side of the laser beam (referred to as a “L0 layer” as occasion demands in the application), to thereby record data into the L0 layer in a heat change recording method (in other words, an irreversible recording method), and it focuses the laser beam, through the L0 layer or the like, on a recording layer located on the rear side (i.e. on the farther side from the optical pickup) viewed from the irradiation side of the laser beam (referred to as a “L1 layer” as occasion demands in the application), to thereby record information into the L1 layer in the heat change recording method.
Patent document 1: Japanese Patent Application Laid Open NO. 2000-311346
Patent document 2: Japanese Patent Application Laid Open NO. 2001-23237